Methods and apparatus for preserving privacy in an rfid system

ABSTRACT

A card comprises an antenna configured to generate and receive radio frequency signals, a chip coupled with the antenna, the chip configured to store sensitive information and communicate the information to an authorized reader via the antenna, and a switching mechanism configured to tune and detune the antenna relative to the chip to enable and disable respectively, the chips ability to communicate the sensitive information via the antenna.

BACKGROUND

1. Technical Field

The embodiments described herein are related to Radio FrequencyIdentification (RFID) systems and more particularly to methods andapparatus to prevent unwanted and/or unwarranted access to informationstored on an RFID chip.

2. Related Art

RFID is an automatic identification method, relying on storing andremotely retrieving data using devices called RFID tags or transponders.The technology requires some extent of cooperation of an RFID reader andan RFID tag. An RFID tag is an object that can be applied to orincorporated into a variety of products, packaging, identificationmechanisms, etc., for the purpose of identification and tracking usingradio waves. For example, RFID is used in enterprise supply chainmanagement to improve the efficiency of inventory tracking andmanagement. Some tags can be read from several meters away and beyondthe line of sight of the reader.

Most RFID tags contain at least two parts: One is an integrated circuitfor storing and processing information, modulating and demodulating aradio-frequency (RF) signal, and other specialized functions. The secondis an antenna for receiving and transmitting the signal. As the nameimplies, RFID tags are often used to store an identifier that can beused to identify the item to which the tag is attached or incorporated.But in today's systems, a RFID tag can contain non-volatile, possiblywritable EEPROM for storing additional data as well.

Most RFID systems use a modulation technique known as backscatter toenable the tags to communicate with the reader or interrogator. In abackscatter system, the interrogator transmits a Radio Frequency (RF)carrier signal that is reflected by the RFID tag. In order tocommunicate data back to the interrogator, the tag alternately reflectsthe RF carrier signal in a pattern understood by the interrogator. Incertain systems, the interrogator can include its own carrier generationcircuitry to generate a signal that can be modulated with data to betransmitted to the interrogator.

RFID tags come in one of three types passive, active, and semi passive.Passive RFID tags have no internal power supply. The minute electricalcurrent induced in the antenna by the incoming RF signal from theinterrogator provides just enough power for the, e.g., CMOS integratedcircuit in the tag to power up and transmit a response. Most passivetags signal by backscattering the carrier wave from the reader. Thismeans that the antenna has to be designed both to collect power from theincoming signal and also to transmit the outbound backscatter signal.

Passive tags have practical read distances ranging from about 10 cm (4in.) (ISO 14443) up to a few meters (Electronic Product Code (EPC) andISO 18000-6), depending on the chosen radio frequency and antennadesign/size. The lack of an onboard power supply means that the devicecan be quite small. For example, commercially available products existthat can be embedded in a sticker, or under the skin in the case of lowfrequency RFID tags.

Unlike passive RFID tags, active RFID tags have their own internal powersource, which is used to power the integrated circuits and to broadcastthe response signal to the reader. Communications from active tags toreaders is typically much more reliable, i.e., fewer errors, than frompassive tags.

Active tags, due to their on board power supply, also may transmit athigher power levels than passive tags, allowing them to be more robustin “RF challenged” environments, such as high environments, humidity orwith dampening targets (including humans/cattle, which contain mostlywater), reflective targets from metal (shipping containers, vehicles),or at longer distances. In turn, active tags are generally bigger,caused by battery volume, and more expensive to manufacture, caused bybattery price.

Many active tags today have operational ranges of hundreds of meters,and a battery life of up to 10 years. Active tags can include largermemories than passive tags, and may include the ability to storeadditional information received from the reader, although this is alsopossible with passive tags.

Semi-passive tags are similar to active tags in that they have their ownpower source, but the battery only powers the microchip and does notpower the broadcasting of a signal. The response is usually powered bymeans of backscattering the RF energy from the reader, where energy isreflected back to the reader as with passive tags. An additionalapplication for the battery is to power data storage.

The battery-assisted reception circuitry of semi-passive tags leads togreater sensitivity than passive tags, typically 100 times more. Theenhanced sensitivity can be leveraged as increased range (by onemagnitude) and/or as enhanced read reliability (by reducing bit errorrate at least one magnitude).

The enhanced sensitivity of semi-passive tags place higher demands onthe interrogator concerning separation in more dense population of tags.Because an already weak signal is backscattered to the reader from alarger number of tags and from longer distances, the separation requiresmore sophisticated anti-collision concepts, better signal processing andsome more intelligent assessment of which tag might be where.

FIG. 1 is a diagram illustrating an exemplary RFID system 100. In system100, RFID interrogator 102 communicates with one or more RFID tags 110.Data can be exchanged between interrogator 102 and RFID tag 110 viaradio transmit signal 108 and radio receive signal 112. RFIDinterrogator 102 comprises RF transceiver 104, which containstransmitter and receiver electronics, and antenna 106, which areconfigured to generate and receive radio transit signal 108 and radioreceive signal 112, respectively. Exchange of data can be accomplishedvia electromagnetic or electrostatic coupling in the RF spectrum incombination with various modulation and encoding schemes.

RFID tag 110 is a transponder that can be attached to an object ofinterest and act as an information storage mechanism. In manyapplications, the use of passive RFID tags is desirable, because theyhave a virtually unlimited operational lifetime and can be smaller,lighter, and cheaper than active RFID tags that contain an internalpower source, e.g. battery. Passive RFID tags power themselves byrectifying the RF signal emitted by the RF scanner. Consequently, therange of transmit signal 108 determines the operational range of RFIDtag 110.

RF transceiver 104 transmits RF signals to RFID tag 110, and receives RFsignals from RFID tag 110, via antenna 106. The data in transmit signal108 and receive signal 112 can be contained in one or more bits for thepurpose of providing identification and other information relevant tothe particular RFID tag application. When RFID tag 110 passes within therange of the radio frequency magnetic or electromagnetic field emittedby antenna 106, RFID tag 110 is excited and transmits data back to RFinterrogator 102. A change in the impedance of RFID tag 110 can be usedto signal the data to RF interrogator 102 via receive signal 112. Theimpedance change in RFID tag 110 can be caused by producing a shortcircuit across the tag's antenna connections (not shown) in bursts ofvery short duration. RF transceiver 104 senses the impedance change as achange in the level of reflected or backscattered energy arriving atantenna 106.

Digital electronics 114, which can comprise a microprocessor with RAM,performs decoding and reading of receive signal 112. Similarly, digitalelectronics 114 performs the coding of transmit signal 108. Thus, RFinterrogator 102 facilitates the reading or writing of data to RFIDtags, e.g. RFID tag 110 that are within range of the RF field emitted byantenna 104. Together, RF transceiver 104 and digital electronics 114comprise reader 118. Finally, digital electronics 114 and can beinterfaced with an integral display and/or provide a parallel or serialcommunications interface to a host computer or industrial controller,e.g. host computer 116.

Today, RFID tags are being incorporated into security documents andidentification devices such as passports and travel cards. Most of theRFID protocols in use today do not require a password or otherauthentication/verification scheme to read information from an RFID tag.Since some of these tags can be read at more than 20 ft, any readeroperating at the same frequency and using the same protocol as the tagcan read the tag's information. Moreover, there are no methods presentlyto detect an unauthorized reading of the tag, so the user would have noidea their information has been read. This is major concern for privacyof the individual or the object which is being tagged.

In some applications, for example, border crossing, it is required toallow a user to conveniently turn on or off the RFID tag. The currentsolution is to use a RF shielding cover. When a user needs to use hisRFID card, with an embedded tag, he will pull it out the RF shieldingcover. But this method depends on the user not forgetting to put thecard back in the shield, and that the user does not lose the shield.Moreover, the user may not be aware of the need for the shield orunderstand how it works and what it does.

SUMMARY

A card comprises an antenna configured to generate and receive radiofrequency signals, a chip coupled with the antenna, the chip configuredto store sensitive information and communicate the information to anauthorized reader via the antenna, and a switching mechanism configuredto tune and detune the antenna relative to the chip to enable anddisable respectively, the chips ability to communicate the sensitiveinformation via the antenna.

A document comprises an antenna configured to generate and receive radiofrequency signals, a chip coupled with the antenna, the chip configuredto store sensitive information and communicate the information to anauthorized reader via the antenna, and a switching mechanism configuredto tune and detune the antenna relative to the chip to enable anddisable respectively, the chips ability to communicate the sensitiveinformation via the antenna.

A method for protecting the privacy of information stored on an RFID tagcomprising an antenna and a chip when communicating the information, themethod comprising controlling a switching mechanism so as to tune theantenna relative to the chip, communicating the information to a readerwhen the antenna is tuned, and controlling the switching mechanism so asto detune the antenna relative to chip after the information iscommunicated to the reader.

A method for tuning an antenna relative to a chip in an RFID tag, theantenna comprising a plurality of portions wherein not all of theportions are in complete electrical communication, the chip comprising aimpedance match circuit, the method comprising configuring a switchingmechanism such that all portions of the antenna are in completeelectrical communication when the switching mechanism is activated andnot in complete electrical communication when the switching mechanism isdeactivated, activating a switching mechanism so as to place allportions of the antenna in complete electrical communication, andconfiguring the impedance matching circuit so as to tune the antennarelative to the chip when the switching mechanism is activated such thatthere is a good impedance match between the chip and the antenna whenthe switching mechanism is activated.

The RFID tag or circuit may be passive or semi-passive. These and otherfeatures, aspects, and embodiments are described below in the sectionentitled “Detailed Description.”

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and embodiments are described in conjunction with theattached drawings, in which:

FIG. 1 is a diagram illustrating an exemplary RFID system;

FIG. 2 is a diagram illustrating an example card including an RFIDcircuit in accordance with one embodiment; and

FIGS. 3 and 4 are diagrams illustrating side views of the card of FIG.2.

DETAILED DESCRIPTION

Most of the RFID chips are designed for supply chain applications likepallet tracking etc. For these applications privacy issues like cloningand skimming etc. are not an issue. But, when these RFID chips are usedto make RFID tags that are then used in security applications like RFIDIdentification cards, passports, visas, etc., privacy becomes bigconcern. Unfortunately, the RFID tags themselves do not incorporate anyprivacy features to prevent unwarranted access to the information storedon the tag. Even passive RFID tags, when used with suitable equipment,are able to read up to 20-30 feet. With such high potential read ranges,there is always a chance of unauthorized access to the informationstored in the RFID chip without such access being noticed by the user.

In the embodiments described below, a switch is included between theantenna and the RFID chip. The switch is configured to tune and detunethe antenna in order to enable and disable the chips communicationcapability. The switch can be activated or deactivated by the user inorder to maintain the privacy of the information stored on the tag.

In order to achieve good performance for a passive tag, there should begood impedance match between the antenna and the chip. Accordingly,various techniques have been developed for matching the antennaimpedance to that of the chip; however, in the embodiments below, thematching must now take into account the position of the switch as wellas other factors as discussed. By taking into account all of thesefactors, an RFID tag can be designed for use in a variety of products,devices, etc., for which privacy is a concern.

The switch can be implemented with a button as a control, or with anyother control mechanism that can enable the switch to be opened andclosed, thereby tuning and detuning the antenna. Thus, a user canconveniently control the RFID tag or card to preserve its privacy whenneeded. For example, the switch can be configured such that it is closedwhen the tag or card is used. When the user needs to present the tag orcard to an authority, the user can press a button to close the switch sothat the tag or card can be read by a legitimate reader. After use, theuser can press the button again to open the switch such that it cannotbe read. In this way, the privacy of the user can be protected.

Such an example embodiment is illustrated in FIGS. 2-4. FIG. 2 is a topview of an identification card 207 that includes an RFID circuitcomprising chip 101 and antenna 203. As can be seen, antenna 203 alsocomprises legs 204 and 206. A button 205 is also included as isconnected with, or comprises a switch mechanism configured to connectlegs 204 and 206 when the button is in the closed position, and todisconnect them when the button is in the open position.

FIG. 3 is a diagram illustrating card 207 with button in the open 205position, and FIG. 4 is a diagram illustrating card 207 when button 205is in the closed position.

Antenna 203 is tuned with button 205, or more specifically the switchingmechanism in the closed position such that legs 204 and 206 areconnected, or more specifically in electrical communication and actingas part of antenna 203. Thus, the impedance matching between chip 101and antenna 203 must be designed to take into account the impedance ofantenna 203 when the switching mechanism and legs 204 and 206 form partof antenna 203.

As a result of the tuning of the impedance match, when the switchmechanism is open, there will be an impedance mismatch between chip 101and antenna 203. The amount of impedance mismatch can be made to vary asrequired by a specific implementation to ensure that there is nounauthorized access to chip 101. For example, in one embodiment, theimpedance of antenna 203 as seen by chip 101 and with the switchmechanism closed can be approximately 20+j110 ohms. But when the switchmechanism is open, then the impedance of antenna 203 as seen by chip 101can be approximately 25−j105. In this example, the reactance part of theimpedance is changing with the position of the switching mechanism. Inother embodiments, the real part of the impedance can be made to changeinstead or in addition to the reactance part of the impedance.

Other effects can also be taken into account to ensure a properimpedance match. For example, in certain implementations, the human bodycan be in close proximity to antenna 203 when the card 207 is used,i.e., when the switching mechanism is closed. As a result, human bodyeffects can be considered during the matching or mismatching of antenna203.

In other embodiments, the antenna can be tuned with the switch in anopen position. Further, the antenna configuration, switch position,etc., illustrated in FIGS. 2-4 is by way of example only and is notintended to limit the embodiments described herein. Still further, whilecard 207 has been described as an identification card, the methods andapparatus described herein can also be implemented in other types ofcards, documents, devices, etc. For example, the embodiments describedherein can also be included in a visa, passport, sensitive document,credit card, etc.

The mechanism for activating the switching mechanism can also takeseveral forms. For example, the activation mechanism can be a positionalswitch, a slide mechanism, etc. The activation mechanism can be any typeof mechanism that allows the antenna to be tuned and detuned as needed.Further, the switching mechanism and activation mechanism can be one inthe same, i.e., the connection between legs 204 and 206, or betweensegments of the antenna, can be a path through the activation mechanism.Alternatively, the activation mechanism can cause a connection, orconductive path to be put in position such that, e.g., legs 204 and 206are conductively connected.

In the embodiment of FIGS. 1-3, antenna 203 was illustrated ascomprising a main portion and two legs 204 and 206 that are not inelectrical communication when the switching mechanism is open. In otherembodiments, more or less legs, as well as other configurations can beused. For example, a single leg that is not in electrical communicationon at least one end with the main portion, i.e., not in completeelectrical communication.

As noted above, elements outside of card 207 can influence the tuning ofantenna 203. One of skill in the art will also understand that card, ordevice 207 can also effect the tuning of antenna 203. For example, ifcard 207 is a credit card or travel card, then card 207 will comprisesome form of plastic substrate which may or may not effect the antennatuning Similarly, if device 207 is a travel document such as a visa orpassport, then the device can comprise one or more layers or pages ofpaper, which may or may not be stored inside of a cover, such as aplastic cover. The paper, cover, etc., may or may not effect the antennatuning Certainly, if device 207 comprises or is affixed to, e.g., metalor glass, then these elements will effect the tuning All of thesefactors should be taken into consideration when tuning antenna 203.

While certain embodiments have been described above, it will beunderstood that the embodiments described are by way of example only.Accordingly, the systems and methods described herein should not belimited based on the described embodiments. Rather, the systems andmethods described herein should only be limited in light of the claimsthat follow when taken in conjunction with the above description andaccompanying drawings.

What is claimed is:
 1. An RFID device for storing and communicatinginformation to an authorized reader, the RFID device comprising: acover; a substrate within the cover; an antenna configured to transmitand receive radio frequency signals; a chip on the substrate coupledwith the antenna, the chip including an impedance matching circuit, thechip configured to store information and communicate the information tothe authorized reader via the antenna; a switching mechanism configuredto connect and disconnect a plurality of portions of the antenna nototherwise in electrical communication with each other to tune and detunethe antenna relative to the chip to enable and disable, respectively,the chip's ability to communicate the information via the antenna; andan activation mechanism configured to control the switching mechanism,wherein the activation mechanism is user-operable; wherein the impedancematching circuit is configured to ensure that when the switchingmechanism is activated, there is a good impedance match between the chipand the antenna, the impedance matching circuit further configured toaccount for the effects of the substrate, the switching mechanism, and asurface to which the device is attached when the antenna is tuned anddetuned via the switching mechanism.
 2. The RFID device of claim 1,wherein the activation mechanism is a button.
 3. The RFID device ofclaim 1, wherein the antenna is tuned with respect to the chip when thefirst and second legs are electrically coupled, and detuned when theyare not.
 4. The RFID device of claim 1, wherein the antenna is detunedwith respect to the chip when the first and second legs are electricallycoupled, and tuned when they are not.
 5. The RFID device of claim 1,wherein the substrate is part of a credit card.
 6. The RFID device ofclaim 1, wherein the substrate is part of an identification card.
 7. TheRFID device of claim 1, wherein the substrate is part of a travel card.8. The RFID device of claim 1, wherein the substrate is part of adriver's license.
 9. The RFID device of claim 1, wherein the RFID devicefurther comprises an activation mechanism configured to control theswitching mechanism, wherein the activation mechanism is user-operable.10. The RFID device of claim 1, wherein the matching circuit is furtherconfigured to account for the cover is attached when the antenna istuned and detached.